Photographic color correction using colored couplers



' 2 Sheets-Sheet 1 ATTORNEYS P. w. VlTTUM ET AL Filed Aug. 30-, 1945 v PHQTOGRAPHIG COLOR (JORRECTION USING coLoimD COUPLERS Sept. 30, 1947 50o WAVELENGTH MILL/MICRONS 0 M m wmm W WJJ m a E A R Q L M ay 1 Y B 1 w v m m v u m, m 2 twig wwutmo w m A p QcfB. 0W 1 o. w J\ ,AWH 3 v I O F 5 0 v 5 V I. \CRimQ #GR G Sept. 30, 1947 P..W. VITTUM ETAL PHOTOGRAPHIC COLOR CORRECTION USING COLORED COUPLERS Filed Aug. 30, 1945 2 Sheets-Sheet 2 FIG.4.

GREEN BLUE RED

. 500 600' WAVELENGTH- M/LL/M/C/MNS xkBzmQ wut o FIG. 5.

L06. EXPO-SURE FIG.6.

PAUL W. V/TTUM REBECC'A J. ARNOLD INVENTORS W. W

, BY Q GREEN BLUE I. O6. EXPOSURE I xhwlma A TTORNE YS Patented Sept. 30,1947

UNITED STATE s FATE 2,428,054 NT" JOF man Kodak Company, Rochester, N. Y., a corporation of New-Jersey I Application August 30, 1945, Serial No. 613,455

4 Claims.

This invention relates to color photography and I particularly to color correction using colored couplers. Color couplers which couple with the development product of primary aromatic amino developing agents to produce colored dye images upon photographic development have been described in numerous prior patents. The use of colored color couplers to secure automatic color correction has been described in Hanson U. S. application Ser. No. 533,910, filed May 3, 1944. These colored couplers are destroyed during coupling, the residual uncoupled portion serving to compensate for the unwanted absorption of the image dyes. The theory of this method requires that the absorption of the residual colored coupler and the undesired absorption of the image dye should be nearly equal. This requirement is not always fulfilled by the colored couplers and introduces errors in the process as pointed out more fully hereinafter.

It is therefore an object of the present invention to provide a novel method of color correction involving the use of colored couplers. A' further object is to provide a method of equalizing the absorption of residual colored coupler. and the undesired absorption of the image .dye in a photographic layer. Other objects will appear from the following description of'our invention. I 1

These objects are accomplished by'incorporating in a silver halide emulsion a mixture of col-' ored anduncolored couplers which produce dye images ofthe same hue on coupling, the proportion of colored to uncolored coupler being such that the absorption of light in the unwanted regions by the final dye'imagesis equal to the absorption of light by the colored coupler.

In the accompanying drawing, I Fig. 1 is a graph showing the absorption of different densities of a typical coupled dye image.

Fig. 2 is a graph showing a series of absorption curves obtained from a typical colored coupler.

Fig. 3 is a graph showing a'series of absorption curves obtained from different densities of the dyes resulting from a mixture of colored and uncolored coupler-according to our invention. Fig. 4 is a graphshowing a series of curves similar to Fig; 3obtained from a different set of couplers.

Fig. 5 is a graph showing the relation between exposure and density of a photographic layer containing a mixture of colored and uncolored couplers according to our invention and Fig. 6

is a graph similar to Fig. 5 for a different set of 55 couplers.

If a silver halide emulsion, containing a'color coupler or not, is exposed under a step tablet and developedwith a primary aromatic amino develcoupler, a series of dye ment process. The color of the original coupler which may be represented as in Fig. 1. If the optical density is plotted at varioustwave lengths, a series of curvessuch-asA to F will be obtained.

zAs represented for a -magenta dye image,- the dye absorbs a'major proportion of light in the green region of spectrum between 500 and 600 mil1imicrons and absorbs a minor proportion of light in the blue region of spectrum between 400 and 500 millimicrons and also absorbs a minor amount of light in' red spectrum regions between.

600 and 700, millimicrons. The absorption of the dye in the blue and the .red spectral regions is undesired and introduceserrors in the color proc- ";ess in which the dyeis used.

According to the invention of the Hanson application, Ser. No. 533,910 the ordinary coupler is replaced by a colored coupler whose color is destroyed duringcoupling in proportion to the amount of the coupled dye formed in the develop,

is chosen so that ltabsorbs light of the same color as the undesired absorption of the dye formed from it. In this way, the colored coupler .Z-Can correct for the improper absorption of the coupled dye and thus effect masking. Depending upon the correction desired, the cyan coupler is colored red, orange or yellow, the magenta coupler is colored yellow or green and the yellow coupler is coloredlmagenta' or blue. The red, orange or yellow coupler used for the oven dye absorbs blue or blueand green light which the cyan dye also absorbs'but which it should transmit. The yellow or green'coupler used for the magenta dye absorbs blue "or red light which the magenta 'dye absorbs butwhich it should transmit. The magenta, coupler used for the yellow dye absorbs green light ,whichthe .yellow dye absorbs to a small extentlbut' which it should transmit. i

The'efiect of using a yellow colored coupler for themagenta dye is illustrated in Fig; 2 of the drawing. If a silver halide emulsion containing the colored coupler'is expose'd'under a step tablet -in the same way as vbefore and developed with a primary aromatic amino developing agent, a series of absorption curves similar to those of Fig. 2 will lee-obtained. Curve A represents the absorption of the uncolored coupler where no ex- 'posure has taken place. Curves B, C and D and Exrepresent increasing amounts of exposure and show' that the resulting dye is a combinationof colored coupler and the dye formed from it.

Curve F represents the greatest exposure and I .the highest density of coupled dye, the colored coupler havingbeen entirely replaced by the coupled dye. n j" Inj order to achieve perf ect masking, the undesired absorption of the final dye; image should oping agent in the presence of an ordinary color" 60 be just cancelled out bythe absorption of the colimages will be obtained Curve A in Fig. 2 shows that the absorption of e the colored coupler in this region is greater than the undesired absorption otmagenta dye in the blue region. This results inso-called over-correction and appears as a reversedimage in yellow dye along with the negative image in magenta dye.

We have found that this undesirable feature of the use of a colored coupler in a photographic emulsion layer may be ov ercome by using a mix ture of colored and :uncolored couplers which produce a dye imagerof the same hue upon coupl n the proportion oi coloredand uncolored coupler being so chosenthatthe colored coupler absrbs lightin the undesired absorption region of the final dye image, in substantially the same amount as the light absorbed .by the maximum amount of coupleddye formed from both couplers. Inthe case of the magenta dye illustrated in Figs. 1 and 2, the amount of colored coupler would be such. that its maximumabsorption in the blue region would not be. greater than the absorption in the blue region of the maximum amount of coupled dyeiormed from both the colored and uncolored couplers.

The eifect of this combination of colored and uncolored couplers is illustrated in Fig. 3 of the drawings. This figure shows the absorption curves obtained upon" an exposure under a. step tablet and development with a' primary aromatic amino developing agent of an emulsion containing a. mixture of colored and uncolored couplers. As shown therein curve -A is the absorption curve obtained from the colored coupleritself, that is, in the region Wherethe're was no exposure. Curves B, C and D of Fig. '3 represent increasing amounts of exposure and increasing dye densities obtained in these regions. "Curve E. represents a maximum dye density where the colored coupler hasbeen entirely replaced by coupled dye. The dyeimages represented by curves B to E are a combination of the dyesj formed from both the colored and the uncolored couplers. The dyes 'formed fromthese, couplers may be identical or ma be similar, theonly requirement being that they'are of the s'ameh'u'e. lThe curves A to E show that in the region of undesired ab.- sorption between 400. and ',500 niillin1icrons, the absorption is substantially constant'for all .of the images. This means thatthe undesired absorption in the blue spectral region has been .efiective- 1y cancelled out since theabsoiption in this region is the same regardlessofthedensity of the dye image in the green spectral region, that is, the region of principal absorption ofIthe final dye.

Fig. 4 shows a similar series of curves obtained from a cyan dye image., In this. case the colored coupler is orange and is represented by curve A. The final cyan dye image of hi g hest density is represented by curveE anddntermediate densities and. combinations of colored coupler and final dye are represented: by curves B to D. The cyan dye image represented by curve-E absorbs ,an appreciable amount-oi light in thebl-ue and green spectral regions from- 4 00.1 to. 600 millimicrons, where it should transmit, and the absorption in these regions is effectively. cancelledv out by the colored coupler. Absorption by the combination of residual colored coupler and cyan dye ima e is 4 substantially constant in theblue and green spectralregions.

It will be noted that the various curves represented in Figs. 3 and 4 do not coincide at every point in the region of undesired absorption. Perfect correction is achieved if the total or integrated absorption throughout the undesired absorption region is the same or substantially the same for a series of dyes or a combination of dyes.

The usefulness of our process in overcoming the undesired absorption of the image dyes will be further evident from a consideration of Figs. 5 and 6 of the drawing. The curves of these figures are densitometric curves of the dye images in various spectral regiens and represent absorption gamma, that is, H and D curve of the dye image as read by light of the primary colors. In Fig. 5 which shows the densitometric curves for a series of dye images such as those represented by the magenta dye of Fig. 3 of the drawing, the dye images were read through green, blue and redrfilters. The curve made through the green filter shows that the dye image obtained by low exposure has low density and that this density increases with increase in exposure. Through the blue and the red filters, the density is substantially constant regardless of exposure. This shows that in the blue and the red spectral regions where the magenta dye has undesired absorption, there is no density variation of the dyeproduced by a series of exposures. Similarly, in Fig. 6 which illustrates the curves obtained with a cyan dye such as that of Fig. 4, the densities obtained through the green and the blue filters are substantially constant while the density when read through a red filter changes with change in exposure.

Since the undesired absorption of the image dyes obtained according to ourinvention do not .'-vary with change in exposure, these densities are theequivalent of a neutral density .over the image and may easily be compensated for by an increase in exposure during printing.

According to our invention, the uncolored coupler may be any coupler well known in the art and may be incorporated in the developing solution or in the emulsion layer. If used in the emulsion layer, suitable means may be used to prevent diffusion of the coupler throughout the layers .of amulti-layer coating.

The colored coupler which wepropose to use may be any of those disclosed in Hanson application, Ser. No. 533,910, or in Glass, Vittum and Weissberger U. S. application, Ser. Nos. 533,930,

filed May 3, 1944. The colcred coupler must be one which is destroyed or decolorizedduringcouplingto form the image dye. This is generally accomplished in the case of the couplers described in the above-mentioned patent applications by the substitution of an azo group in the position in the coupler molecule which is active in the couplingreaction. The

colored coupler must be one which produces a dye of the same hue as the-uncoloredcoupler, although the dyes need not be of identical'composition. j 5

The couplers maybe incorporated inthe sensitive silver halide emulsion by dissolving the so dium salt .of the .coupler in the emulsion or they may be incorporated by dissolving them in a We.- ter-insoluble, water-permeable solvent for'the coupler-as described in Mannes and Godowsky U; S; 2,304,9540 granted December 15, 1942, or

Jelley and Vittum 2,322,027, granted June 15, L943.

The following examplesxillustrate the incore I l-hy droxy-2-[p-(p tert. butylpheuoxy)-phenyl]-naphthamide Coloredcouple'r v CCH:

l-hydroxyi- (o -methoxypheny1azo) 2- [p (p -tert. butylphenoxy) phenyH-naphthamide Seven grams of the uncolored coupler and 3 grams of the colored coupler were dissolved in 22.5 grams of tri o-cresyl phosphate by gentle warming and this solution was emulsified with 40 cc.

of 2-% gelatin solution containing 1.5 grams of tri-isopropyl naphthalene sulfonate (Alkanol B) by passing the whole mixture through a colloid mill several times. The resulting emulsion was added to 1000 cc. of a melted silver halide emulsion. If used in a multi-layer coating, this emulsion can be sensitized to red light since the couplers produce cyan dye images.

Example 2 An emulsion'was prepared in the same way as Example 1 using 7.5 grams of the following uncolored coupler and 2.5 grams of the following colored coupler:

Uncolored coupler- 4.6-dichloro-5-methyl-2-(p-tert. emylphenoxy-acetamlde)phenol Colored coupler- 1'hydroxy-4-phenylazo-2-[p-(p'-tert. butylphenoxy)-phenyl]- nephthamide Example 3 An emulsion was prepared in the same way as Example 1 using 8 grams of the uncolored coupler used in Example 2 and 2 gramsofthezfollowing colored coupler.

Colored coupler-r Ct u , 51(p-sec.amyl)-phenylsulionamide-4-p-tert.amylphenoxyphcnylazoH-naphthol I,

{Example 4 An'emulsion was preparedin the same way as Example 1 using? grams of the uncolored coupler used in Example '2; 1.2 grams of the following 001- ored'couplerfAand 1.8 grams of the following colored coupler B.

Colored coupler A- I CsHu l-hyd1'ozy-4-phenyIazo-2-(N-isoamyD-naphthanilide I I Colored coupler B I I H I Q ocHl 1-l1ydroxy-4 (2-methoxy-4-nitrophenylazo)-- --2-(4-tert;,butylphenoxy)-naphthanilide 1 Example 5 An emulsion was prepared in thesame way as in-Example 1 using 7 grams of the following uncolored coupler and 3 grams of the following'col ored coupler.

Uncolored coupler- N=CNHC O-C Her l-phenyl-Ii-palmitylamino-fi-pyrazolona Colored coupler- N: C C 15H3l l-phenyl-3-n-pentadecyl-4-p-acetamino-phenylazo-5-pyrazolone Upon exposure and development of these lay-- ers in a color developer such as the following, the": emulsions of Examples 1 to 4 produced cyan dyes:

7 andcthe: emulsion-10f:Example:5iiproduced1amae genta dye; 7 2 amino -diethylaminotoluene hydroohloe The time of development depends upon the nature of the-particular-silver halide;emulsions,-employed. Development is followedby an acid, hardening fixing bath and a silver removal bath according to well-known practices.

The relative proportions of the colored and uncolored couplers in the mixture cannot be stated numerically but may be readily determined from the spectral absorption curves such as those of Figs. 3 and 4 or from densitometric curves such as those of-Figslfiandfi; If theproportions are correctly chosen, there will be no over-correction but the colored coupler will absorb light in the unwanted spectral, region ofthe final dye in substantially the same; amount as that absorbed by the maximum amount of. coupled j dye produced by both couplers on development. In gen- 25 eral; the colored coupler will be present in an amount between and 50%" of" the total amount of colored and uncolored couplers.

The colored couplers described in the specific examples above are similar to those described in Glass, Vittum and Weissberger U. S. applications, Ser. Nos. 533,931 and 533,932 and are prepared as described in those applications.

It will be understood that themoditications and examples described herein are illustrative only and that our inventionjs to be taken as limited only by the scopeof the appended claims We claim:

1. A sensitive photographic silver halide emul sion layer containing a colored coupler whose color is destroyed upon coupling and an uncolored coupler, both being capable of forming a dye im-, age of the same hue upon-coupling with the de velopment product of a primary aromatic amino developing agent, said dye imagea-bsorbing' a major proportion of light in the spectral. region of one of the primary colors and a'nrinor proportion of light in another region of the-visible spectrum, the ratio of amounts of saidcoloredcoupler to said uncolored couplers being, such that the degree of color development does not substantially change the optical density ofthe layer for light of said; other spectral region;

Arsensit ve p t raphic silvenhalidelemulsion-- layer containing a colored; coupler; whose; 5 2,340,656

8 Li: color-isdestroyedupon coupling and an uncolored coupler, both being capable of forming a cyan dye image, upon coupling with thedevelopment prod not of a primary aromaticamino developing 2 5 "agent, said dye image absorbing a major proportion-of red light and a; minor proportion; vof blue and green light, the ratio of amounts, o:said; colored coupler to said uncolored coupler being such that the degree of color development does 10 not substantially change the optical density of the layer for said-blue and green light.

3;, A sensitive photographic silver halide emulsion layer containing a colored coupler whose; color is destroyed upon coupling and an uncol-- 'ored coupler, both being capable of forming a magentaldye image upon coupling-with the development product of a primary aromatic amino developing agent, said dye image absorbing a major proportion of green light and a minor prod. portion of blue-light, the ratio of amounts of said colored coupler to,-said uncoloredcoupler being; such that the degree of color development does not substantially change the optical densityrof the layer for said blue light.

4. The method of forming a color-correcting color separation image in a silver halide emulsion layer, which comprises incorporating in said layer a colored coupler whose color is destroyed upon coupling and an uncolored coupler; both couplers -tbeing capableof forming a dye image of the same hue upon coupling with the development product of a. primary aromaticvamino developing agent,v

exposingsaidlayergand. developing it with a pri-. mar aromatic amino developing agent to form.

dye images; of: the same hue absorbing a major,

proportion of lightin-the. spectral region of one 1 of the primary colors and aminor proportion oflight in another region of the visible spectrum; the. ratio, of amounts of -;said colored coupler tov ksaid uncolored coupler-being such thatthe degree ofv color, develo innentr does not substantially, change the optical density of the layer for light.- of said other spectral..regi on..

455 PAUL W. VI'ITUM.

"file of this patent:

UNITED STATES PATENTS Number 

